1. Field of the Invention
The present invention relates to a MPEG2 (Motion Picture Expert Group-2) transport decoder, and more particular to a data input/output apparatus of the MPEG2 transport decoder for storing packet data in a memory during decoding of a transport, and for outputting the decoded packet data to video/audio decoders.
2. Discussion of Related Art
In general, the transport decoder inputs a transport input stream from a FEC(Forward Error Correction) part and a format of a DSM, and selects the packet required during the decoding of the video/audio decoders to perform a transport header decoding, an adaptation field decoding, and a packetized element stream header decoding.
Further, the transport decoder stores the decoded data in a transport memory and outputs video/audio compression data to the video/audio decoders.
FIG. 1 is a construction diagram of a data input/output apparatus of a transport decoder according to the prior art. Referring to FIG. 1, there are provided in FIG. 1 an input buffer 1, a transport packet decoder 5, video and audio buffers 3 and 4, a buffer 2 for PSI/PGI, a transport memory 7, and a transport memory interface controlling part 6. The input buffer 1 temporarily stores transport input stream and outputs it. The transport packet decoder 5 decodes the transport input bit stream from the input buffer 1 according to a transport packet method, and outputs the video/audio compression data and PSI/PGI data, respectively. The video and audio buffers 3 and 4 temporarily store the video and audio compression data outputted from the transport packet decoder 5 and then output the data to the video/audio decoders. The buffer 2 for PSI/PGI temporarily stores and outputs the PSI/PGI data outputted from the transport packet decoder 5. The transport memory 7 stores the data outputted from the buffer 2 according to an address control signal and a read/write control signal. And, the transport memory interface controlling part 6 provides the address control signal and the read/write control signal.
The operation of each of the parts of FIG. 1 is as follows.
First of all, the input buffer 1 receives the transport input stream and inputs the transport input stream to the transport packet decoder 5 for the transport packet decoding. At this time, the transport input stream can be inputted as a burst mode, or can be inputted with a consecutive clock signal. Further, the transport packet decoder 5 selects the packet needed in the decoding of the video/audio decoders and then performs the transport header decoding, the adaptation field decoding, and the PES header decoding. Thereafter, the video and audio compression data are transferred to the video/audio decoders (not shown) through the video and audio buffers 3 and 4, and the PSI (Program Specific Information) data and the PGI(Program Guide Information) data are stored in the transport memory 7 through the buffer 2 for PSI/PGI.
The video/audio data are outputted to the video/audio decoders through the video and audio buffers 3 and 4 whenever decoded in the transport packet decoder 5. The address and read/write control signals of the transport memory 7 are generated from the transport memory interface controlling part 6 and then provided to the transport memory 7.
In the meantime, the address areas of the transport memory 7 for storing the PSI and PGI data are determined by an internal register of the transport memory interface controlling part 6, and the transport memory 7 generates the address and control signals so that the PSI and PGI data can be stored in the determined areas.
Therefore, the address map of the transport memory 7 is shown in FIG. 2. In order words, PSI 1 data is stored in addresses AA . . . A to BB . . . B, and PGI 1 data is also stored in addresses aa . . . a to bb . . . b-1.
However, the data input/output apparatus of the transport decoder according to the prior art stores the packet data in the input buffer 1, and the transport packet decoder 5 decodes the input data. At this time, if a decoding time is long in the transport packet decoder 5, there may arise overflow in the input buffer 1 because the input buffer 1 stores the transport input stream to be consecutively inputted. Further, in order to prevent the overflow, there may arise the other problem in that the input buffer should be large in its capacity. Furthermore, even though the decoding time is short in the transport packet decoder 5, if the decoded video/audio data are not normally outputted through the video and audio buffers 3 and 4 because of the decoding delay of the video/audio decoders, there also may arise overflow in the video and audio buffers 3 and 4. Moreover, according to the prior art, the use of a fixed memory map of the transport memory interface controlling part 6 reduces efficiency of the transport memory.